After upgrading the ESXi host to 4.1 and upgrading VMs to VMwareTools to 4.1, you may experience slow TCP performance on VMs running on the 4.1 ESXi host. You can address this situation by disabling Large Receive Offload (LRO) on the ESXi host. See further below.

Note:

If you're running CUCM 8.6, UCCX/ IP IVR 9.0 and above (i.e., UC applications using VOS/ RHEL 5+), the Linux version used in these releases is compatible with LRO, you don't have to worry about the settings (disable LRO is not required) on the host or which version of ESXi is running. However, Disabling LRO is required for CUCM including other UC applications such as UCCX/ IP IVR, etc. versions 8.0 and 8.5 (prior to VOS/RHEL 5.0) irrespective of ESXi version.